The present invention relates generally to the field of photographic projection devices such as motion picture projectors or slide transparency projectors, and is more specifically directed to the arrangement within such projectors for producing automatic focusing of the transparency image on a remote viewing screen.
The use of automatic focusing systems for causing movement of a projection (objective) lens along the optical axis in either motion picture projectors or slide transparency type projectors are well known in the art. Typical in such arrangements are the provision of an objective lens carried within a lens barrel, the barrel being mounted for axial movement within a sleeve which is also arranged for axial movement along the optical axis. In automatic focusing systems means are provided for detecting variations in the distance between the objective lens carried within the barrel and the projection screen, and between the transparency and the objective lens. Sampling beams of light are typiclly provided so as to be reflected from the screen and or the transparency upon detection means frequently carried on the sleeve. The detection devices generate electrical signals responsive to displacement in such sampling beams in order to drive motive means for causing axial displacement of either the objective lens or the lens sleeve. Such axial displacement is effected in order to correct errors in the distances between the objective lens and the transparency so that proper focusing can be automatically effected. One such example of this type of automatic focusing mechanism may be found in U.S. Pat. No. 3,813,155.
The motive means for causing axial displacement of the objective lens, in response to detection error signals indicating need for displacement to effect automatic focusing, may be found by a variety of arrangements. One such arrangement, shown in the above mentioned patent, involves the use of a lens barrel mounted within a sleeve which is carried on the projector housing for axial reciprocal movement. The sleeve carries an axially extending gear rack for meshing engagement with a pinion gear which is driven by a shaft of a reversible electric motor, which is also mounted on the housing of the projector. Energization of the motor will cause the pinion to drive the rack thus producing axial reciprocal movement of the lens barrel sleeve. This type of arrangement, while relatively simple, has the disadvantage of requiring a large amount of space within the projector necessitating larger housings and costlier assembly procedures.
Other arrangements for effecting focusing adjustment of the objective lens by automatic focusing systems have involved the use of a lens carrying sleeve and a pin eccentrically mounted on a rotatable disc or on a pivotable lever and engageable with following means on the sleeve. The lens adjustment mechanism typically includes a pin or lug eccentrically mounted on a rotatable disc. A recess or groove in the sleeve carrying the lens for receiving the pin or lug forms the following means. Upon rotational movement of the disc, consequent eccentric movement of the pin or lug will cause axial displacement of the lens sleeve so as to effect the desired focusing. This type of arrangement also suffers from similar disadvantages as the previous described arrangement.
Another known device for producing axial displacement of the lens sleeve is shown and described in German Auslegeschrift 1,081,249 published on May 5, 1960. This arrangement provides for the lens sleeve to be connected with a curvilinear guide arranged for movement within the projector housing which in turn is driven by a reversible motor mounted on the projector housing. The curvilinear guides provided in this arrangement may be spiral grooves formed on two discs arranged for supporting opposite sides of the lens sleeve. A pin carried by the sleeve is arranged for engagement with the grooves, so that upon rotational driving of the discs, axial displacement of the lens sleeve will result. This arrangement has the advantage of utilizing a reduced ratio of the drive movement but still suffers the same disadvantages as the previous described arrangements.
It is accordingly one object of the present invention to provide a driving mechanism for producing axial reciprocal displacement of the objective lens carrier or sleeve in order to effect automatic focusing which overcomes the disadvantages of the prior art arrangements.
It is a further specific object of the present invention to provide in a slide or motion picture projector apparatus a compact and space-saving arrangement for effecting automatic focusing by movement of the objective lens carrier.
Yet, another object of the present invention is the provision of a focusing system in which the motive means for causing desired axial displacement of the objective lens is produced by a compact arrangement in which the reversible drive motor is carried directly on the sleeve for translating rotational movement thereof to axial movement of the sleeve to effect desired focusing.
The above objects, features and advantages, along with other objects, features and advantages, of the present invention will become more apparent from the detailed description of the invention, in conjunction with the accompanying drawings to be described more fully hereinafter.